Fluorocarbon based fluids have found widespread use in industry in a number of applications, including as refrigerants, aerosol propellants, blowing agents, heat transfer media, and gaseous dielectrics. Because of the suspected environmental problems associated with the use of some of these fluids, including the relatively high global warming potentials associated therewith, it is desirable to use fluids having low or even zero ozone depletion potential, such as hydrofluorocarbons (“HFCs”). Thus, the use of fluids that do not contain chlorofluorocarbons (“CFCs”) or hydrochlorofluorocarbons (“HCFCs”) is desirable. Furthermore, some HFC fluids may have relatively high global warming potentials associated therewith, and it is desirable to use hydrofluorocarbon or other fluorinated fluids having global warming potentials as low as possible while maintaining the desired performance in use properties. However, the identification of new, environmentally-safe, mixtures is frequently complicated by the need and/or desire to achieve a composition with such a diverse set of properties.
With respect to heat transfer fluids, it is desirable in many different situations to selectively transfer heat between a fluid and a body to be cooled or warmed. As used herein, the term “body” refers not only to solid bodies but also other fluid materials, which take the shape of the container in which they exist.
One well known system for achieving such transfer of heat achieves cooling of a body by first pressurizing a vapor phase heat transfer fluid and then expanding it through a Joule-Thomson expansion element, such as a valve, orifice, or other type of flow constriction. Any such device will be referred to hereinafter simply as a Joule-Thompson expansion element, and systems using such an element are sometimes referred to herein as Joule-Thompson systems. In most Joule-Thomson systems, single component, non-ideal gasses are pressurized and then expanded through a throttling component or expansion element, to produce substantially isenthalpic cooling. The characteristics of the gas used, such as boiling point, inversion temperature, critical temperature, and critical pressure effect the starting pressure needed to reach a desired cooling temperature. While such characteristics are all generally well known and/or relatively easy to predict with an acceptable degree of certainty for single component fluids, this is not necessarily the case for multi-component fluids
Because of the large number of properties or characteristics which are relevant to the effectiveness and desirability of a heat transfer fluid in particular but to many other fluids in general, it is frequently difficult to predict in advance how any particular multi-component fluid will perform as a heat transfer fluid. For example, U.S. Pat. No. 5,774,052—Bivens discloses a combination of difluoroethane (HFC-32), pentafluoroethane (HFC-125) and a small amount (i.e., up to 5% by weight) of carbon dioxide (CO2) in the form of an azeotropic fluid that is said to have advantages as a refrigerant in certain applications. More particularly, the multi-component fluid of Bivens is said to be non-flammable and, due to its azeotropic nature, to undergo relatively little fractionation upon vaporization. However, applicants appreciate that, the fluids of Bivens are comprised of relatively highly-fluorinated compounds, which are potentially environmentally damaging from a global warming perspective. In addition, obtaining fluids with azeotropic properties can sometimes add significantly to the cost of such fluids when used as refrigerants.
U.S. Pat. No. 5,763,063—Richard et al. discloses a non-azeotropic combination of various hydrocarbons, including HFC-32, and carbon dioxide which form a fluid said to be acceptable as replacements for chlorodifluoromethane (HCFC-22). In particular, the Richard et al. patent teaches that the vapor pressure of this fluid is substantially equal to HCFC-22, which is only about 83 psia. Therefore, while the fluid of Richard et al. is expected to perform well in certain refrigeration applications, it may be considered inadequate in the same types of applications mentioned above with respect to the Bivens fluid.